Great question -- I would love to know, too, but I imagine that the # varies wildly. I heard that this year the buying (I think that's what it's called) went really well for RM (that's the process through which retailers put in their orders for upcoming season's bags) and so that might have something to do with the shortage of certain bags now.
Have you tried calling the stores that don't post all or any of their RMs online, like Saks, Bloomie's Nordie's or Neiman's? They can generally find bags for you, though you won't get that much of a price break most of the time, unless you get lucky w/ a Bloomie's sale (though I doubt the lizard/iris bags will be around at that point).
And there's always the 'bay...